I went into Settings->Privacy->Factory reset and checked "Format USB Storage". Then I pressed the button to continue and it prompted for my PIN (just numbers) as usual. Then it said it was formatting the USB storage as I told it to. And then it just shut off. So I started it back up and it prompted for a password (full keyboard; any characters you want).

I don't know what I had set that password to (I haven't used that kind of a password in a while) so now I'm stuck. Going into recovery mode does the same thing. Download mode works just fine.

So now what do I do? Is there some way I can format /data manually from my computer?

Since I don't know what the password is, I played around with it and failed enough times that it told me that if I failed one more time I could lose data on the SD card. So I failed one more time (I didn't care about the SD card) and it did the reset just fine.